The present invention relates to pilot light testing circuits for machines or other systems and more particularly to a circuit for simultaneously testing all of the pilot lights on a panel.
On modern machinery there are many applications where multiple indicator or pilot lights are used. The lights normally are energized and thus turned on when the electrically operated machine or system they are in circuit with is put into operation. In that manner, the operator can turn on the machinery at a remote location and by means of the indicator light determine whether or not the machine or system is operating.
If the indicator light does not illuminate when the main power switch is activated to turn on the machine or system, it is difficult to determine whether it is the machine or system which is not operating or it is the indicator light which is burned out. Thus it is advantageous to have a means of rapidly testing the indicator lights to determine whether the lights are operational. It is also advantageous to test many or all of the pilot lights simultaneously by activating a single switch or pushbutton.
There are several known methods of testing pilot or indicator lights. In one system, the lens of each pilot light must be depressed to test the light. This is an inefficient and time consuming operation, however, as frequently large controls panels in modern plants and factories contain hundreds of lights.
Another known testing system involves the use of solid state circuitry utilizing diodes, resistors and capacitors. Although various methods have been developed which utilize a single pushbutton for simultaneously testing a plurality of pilot lights with solid state circuitry, these methods are undesirable for safety reasons. In many of these systems, the light and thus the potential that the operator is exposed to is in the order of sixty volts. Further, solid state testing devices have been known to fail due to extraneous signals causing diode shorting; this in turn produces a dangerous feedback into the control circuit.
Another testing system uses diodes in combination with an internal transformer for each light on the panel and one externally mounted transformer for each panel. Similar to the solid state circuitry systems described above, this system is undesirable because of the possible diode failure feedback that results. Also with this known system, each testing device is typically equipped with four wiring terminals requiring significant expense and labor for installation. The necessity of having an additional transformer for the panel also requires significant additional expenses and installation difficulties.
The present invention is an improvement over known pilot light testing systems. The present invention provides for simultaneous testing of all the pilot or indicator lights on a panel; this eliminates the time consuming and costly individual testing of the lights. When the test button or switch is activated, all of the lights not already turned on due to the operation of the machinery or system in the control circuit, will light up. Thus, the operator instantly is informed of faulty indicator lights.
The present indicator light testing circuit may be activated at any time even when the machinery, equipment or systems are operating. Also, the inventive system and circuit eliminates electrical feedback of the test circuit into the main control circuit.
In the preferred embodiment of the invention, each of the pilot light units includes a transformer and a relay-operated, two pole, switching device. The switching device includes a relay coil and a two-pole switch having a switch contact which is movable upon energization of the coil. The movable contact is connected to one end of the primary winding of the transformer, is normally biased into engagement with one pole, and is movable upon energization of the coil into engagement with a second pole. The pilot light unit has three terminals; a signal terminal, a test terminal and a line terminal. The signal terminal is connected to the normally-connected pole of the relay switch so as to be normally connected to the one end of the primary winding of the transformer; the test terminal is connected in common with the other pole of the relay switch and one end of the relay coil; and the line terminal is connected in common with the other end of the primary winding of the transformer of the other end of the relay coil.
In use, the signal terminal is connected to monitor respective controls and receives a current upon energization of the respective monitored control. The test terminals are connected in common to a test switch to receive a test current upon closure of the test switch. The line terminal is connected to one terminal of a power supply. In the preferred embodiment, the line terminal is connected to the ground terminal of the power supply. Since the movable contact is normally engaged with the signal pole, any energization of the monitored control will provide a current to the primary winding through the relay switch which in turn induces a secondary current to energize the pilot light. Upon closure of the test switch, the relay coil is energized to move the movable contact from the one pole to the other pole. A portion of the test current is provided to the primary coil of the transformer to induce a secondary current which energizes the pilot light. Hence, the closing of the test switch provides several functions. It simultaneously energizes each of the relay coils to simultaneously disconnect all of the signal terminals from the primary winding of the transformers. Also, through energization of the relay coil, it connects the primary winding to the test terminal. Furthermore, the test current simultaneously energizes all of the pilot lights. Importantly, the possibility of feeding test current back through the signal terminal is virtually non-existent since the switch is not connected to receive the test current until after the signal connection is interrupted.
The present invention also utilizes reliable electromechanical relay and transformer units which for purposes of the present invention have many advantages over solid state systems (as described above).
Other objects, features and benefits of the present invention will become apparent from the accompanying drawings and the description and claims contained herein.